High pressure roller grinders for grinding rock and the like are for obvious reasons subjected to a high level of wear from the processed material. Each roll of a roller grinder therefore commonly utilizes an outer cylindrical grinder shell made of a wear resistant material covering the rolls. The grinder shell eventually has to be replaced when worn down by the processed material, causing an interruption of the operation of the equipment.
The grinding or crushing shell has to be tightly mounted around the hub portion of the shaft, with a high friction between the parts to avoid loosening of the shell during operation of the grinder. The hub portion of the shaft may have a cylindrical shape or may be slightly conical to enable easy mounting and dismounting of the grinder shell. The conicity is preferably minimal, to prevent the grinding shell from being undesirably released during operation of the grinder.
In a known constructive solution, the outer grinding shell is designed to be mounted around the hub portion of the shaft by means of thermal expansion-contraction. The outer grinding shell is heated to present a thermal expansion sufficient to allow it to axially slide around the shaft, until reaching the mounting position, in which its cooling and shrinkage produce its retention, by high interference, around the hub portion of the shaft, the hub portion being generally cylindrical.
This known mounting solution presents some inconveniences. The outer grinding shell can crack upon cooling, particularly when it is made of a hard high carbon steel, and it can lose its uniformity and its cylindrical tubular geometric form, due to the stress caused by application of heat. The mounting solution by thermal expansion-contraction of the outer grinding shell also presents inconveniences when dismounting the grinding shell from the hub portion of the shaft. The dismounting is extremely difficult due to the high level of frictional interference between the two parts. This difficulty is so great and time consuming that it is frequently preferred to replace the whole shaft-grinding shell assembly, undesirably increasing the costs of replacing the already worn out grinding shells. This problem is particularly cost inducing when the frequency of these replacements is high due to a high level of wear of the outer shell. It is also frequent, in such cases, that the shaft is damaged during the dismounting procedure, further increasing the replacement costs of the grinding shell. In many cases, the bearings, which are usually an expensive part, are integrated in the shaft assembly, further increasing the cost of the replacement when not being able to dismount the outer shell.
There are also known mounting solutions which utilize an internally conical grinding shell operating around a wedge provided between the hub portion of the shaft and the grinding shell and which is forced towards the central region of the roller, producing inward and outward radial forces against the shaft and against the grinding shell, respectively, producing the necessary high level of frictional interference between the grinding shell and the shaft. Although overcoming the inconveniences related to the mounting by thermal expansion-contraction, the utilization of a wedge and an internally conical grinding shell presents the inconvenience of making the axial and radial alignments difficult and the replacement operations of the grinding shell complex and costly.
U.S. Pat. No. 5,060,874 describes a mounting solution according to which each shaft medianly carries a pair of externally conical hubs, each being operatively associated with shrink discs, wedges and an expansion ring, to establish a high level of frictional interference between the grinding shell and the shaft, without requiring thermal expansion-contraction of the recipient. This prior solution requires a large number of components, which undesirably raises its cost.